The present invention relates to intake air separation systems for internal combustion engines, and more particularly, to an intake air separation system that includes an air separation membrane adapted to produce a stream of oxygen enriched air and nitrogen enriched air from the intake air in the presence of a stream of exhaust gas purge air.
Exhaust emission regulations have become increasingly restrictive, and internal combustion engine manufacturers are faced with competing interests in having to meet the emissions requirements while providing acceptable engine performance, including fuel efficiency. Exhaust emissions include visible smoke, particulate matter and oxides of nitrogen (NOx). Particulate matter includes unburned hydrocarbons and soot, while NOx emissions are a somewhat indefinite mixture of oxides of nitrogen, which may include primarily NO and NO2. Many approaches have been used to address emissions issues, including fuel injection, combustion control strategies and systems, after treatment systems and exhaust gas recirculation (EGR) systems.
Unfortunately, attempts at solving one issue can have a negative impact on others. For example, emission reduction systems often have a negative effect on fuel efficiency. To improve fuel efficiency, or power density, it is known to increase the amount of oxygen in the combustion chamber. This has been done in the past by pressurizing the combustion air provided to the combustion chamber. Pressurization of the combustion air increases the oxygen available for combustion. Turbochargers have been used for this purpose.
Particulates are formed in the combustion cycle primarily during relatively early portions of the cycle, but are usually burned as temperature and pressure increase during the combustion cycle. Particulates entering the exhaust stream tend to be formed in the latter part of the combustion cycle, as the pressure and temperature decrease. Increasing the oxygen content of intake air tends to reduce the quantity of unburned hydrocarbons by increasing the likelihood of complete combustion.
After treatment of exhaust gas can be used to reduce the amount of unburned hydrocarbons by continuing oxidation of the unburned hydrocarbons. A secondary air supply can be provided to the exhaust stream. The already high temperature of the exhaust stream will support further combustion with the introduction of additional oxygen in the exhaust gas stream. A trade-off occurs in that while particulate matter may be reduced, the further oxidation creates still higher temperatures in the exhaust system. The design of exhaust systems for these higher temperatures requires components able to withstand a much hotter environment. Such components are often heavy and expensive, and may require more frequent servicing.
Decreased fuel consumption and decreased particulate production often go hand-in-hand. However, at the same time, NOx production often increases. NOx forms when nitrogen mixes in a high temperature environment with excess oxygen not used in the combustion process. Therefore, while excess oxygen and high combustion temperatures are beneficial in reducing fuel consumption, the same combination is detrimental in terms of increased NOx formation. Engine manufactures must strike a delicate balance whereby NOx production, fuel consumption and particulate matter formation are controlled to meet emissions regulations and engine user demands.
NOx reduction has been accomplished using exhaust gas recirculation (EGR). By introducing EGR flow to the combustion chamber, the amount of available oxygen for formation of NOx is reduced. By reducing the amount of oxygen, the combustion process is slowed, thereby reducing the peek temperatures in the combustion chamber. EGR systems typically use exhaust gas, but may also use enriched nitrogen sources.
U.S. Pat. No. 6,289,884 xe2x80x9cINTAKE AIR SEPARATION SYSTEM FOR AN INTERNAL COMBUSTION ENGINExe2x80x9d issued Sept. 18, 2001, discloses a method and system for intake air separation in an internal combustion engine. An intake air separation device utilizes a membrane to separate the intake air into a flow of oxygen enriched air and a flow of nitrogen enriched air. A purge air circuit is used to deliver a flow of sweep air or purge air to the intake air separation device, thereby increasing the effectiveness of the air separation. Several modifications of the system are shown, each using intake air as the purge air stream in the intake air separator. When intake air is used as the purge air stream, higher oxygen flux is achieved, but is coupled with higher nitrogen flux. If it is desired to yet further increase the oxygen flux, a larger membrane surface is required, requiring a larger separation device, and the increased oxygen flux will be coupled with a corresponding increased nitrogen flux. It may be desirable in some instances to increase oxygen flux in a relatively small separator device and/or to increase oxygen flux without a corresponding increase in nitrogen flux.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an intake air separation system is adapted for providing a nitrogen enriched air stream for a combustion process within an internal combustion engine having an exhaust system. The intake air separation system is provided with an intake air input adapted to receive intake air used in the combustion process for the engine. An intake air separation device is in flow communication with the intake air input, and is adapted for receiving the intake air and separating the intake air into an oxygen enriched air stream and a nitrogen enriched air stream. A purge gas conduit is in fluid communication with the intake air separation device and with the exhaust system, and is adapted for providing a stream of exhaust gas as purge gas flow to the intake air separation device, to increase efficiency of intake air separation.
In another aspect of the invention, a method of controlling an intake air flow for an internal combustion engine having an intake air system providing intake air to an intake manifold and one or more combustion chambers, and an exhaust gas system receiving exhaust gas flow from the combustion chambers is provided with steps of providing an intake air separating device; directing the intake air to the intake air separating device; in the air separating device, dividing the intake air into an oxygen enriched air stream and a nitrogen enriched air stream, and directing at least some of the flow of exhaust gas through the intake air separating device, as purge gas flow, to increase the efficiency of the step of dividing the intake air.
In still another aspect of the invention, an internal combustion engine is provided with an intake manifold, a combustion section including a plurality of combustion chambers, and an exhaust system including an exhaust conduit. An intake air separation system is adapted for providing a nitrogen enriched air stream for a combustion process within the plurality of combustion chambers. The intake air separation system is provided with an intake air input adapted to receive the intake air used in the combustion process for the engine. An intake air separation device is in flow communication with the intake air input, and is adapted for receiving the intake air and separating the intake air into an oxygen enriched air stream and a nitrogen enriched air stream. A purge gas conduit is in fluid communication with the intake air separation device and with the exhaust system, and is adapted for providing a purge gas flow of exhaust gas from the exhaust system to the intake air separation device, to increase efficiency of intake air separation;